Japanese patent document 61-94705 describes a method of regenerating and recycling polystyrol granules from refuse containing polystyrene foam, where this refuse is heated enough that it almost melts, thereby reducing its volume substantially and greatly condensing it so that the material can be comminuted in a crusher. A modifier containing anorganic components such as lime or clay, aluminum hydroxide, wood chips, rubber, or plastic is mixed with polystyrene granules or polystyrene-resin powder. The mixture is pelletized by means of an extruder to recover polystyrene resin. This process is extraordinarily expensive and produces a very mixed end product whose further use is very limited in particular because of the high costs of the treatment method.
Japanese patent document 21-1307 describes an apparatus for improving the quality of a reusable product of foamed polystyrene refuse. The refuse is cut by electrically heated wires into small pieces and these are dropped for shrinking into a container where they are defoamed with low-pressure steam at a temperature between 120.degree. and 160.degree. C. and pressures between 3 and 6 bar and are reduced in volume. Then the product is fed to a mill and is ground to particles with a particle size between 10 and 30 mm.
German patent document 1,268,813 describes a machine for mixing and plastifying thermoplastic resins which has a mixing drum provided with a fast-moving mixer and in which the plastification takes place exclusively from the frictional heat generated in the mixer. The mixing machine is provided with a comminuter for polyvinyl chloride films or for particular polyvinyl chloride refuse. A selective comminution of refuse containing different types of plastics is not possible with this machine.
The publication "Kunststoffe" (80; 1990, 3, Carl Hanser Verlag, Munich 1990, page 310) discusses the direct recycling of refuse during the manufacture of films." It states that production is not possible without refuse. It is therefore important to act directly on production refuse before it has a chance to get dirty. With plastic film this is particularly important because the production costs are largely dominated by the material costs. The possibility of recycling edge trimmings and rejected film is described in the cited passage. This procedure relates to a particular type of refuse recycling intimately related to the production of plastic films. This makes it to a degree possible to seek a machine solution and is therefore not applicable to the recycling of unsorted and partly dirty plastic refuse as is produced in the sector of private households and chain businesses and the like in connection with packaging trash.
British patent document 1,313,203 describes a method and apparatus for condensing particles of plastic foam. They are fed onto a vibrating cold surface which moves them through a heating area so that they collapse and partially fuse together but do not stick to the transport surface. The cooked-together mass is fed between a pair of cooled compression rollers and is thereby reduced to a consistency of 400 g/l. Then for further use cylindrical pellets are created by extrusion with a density of 560 g/l. This method is limited to treating thermoplastic hard-foam particles and necessitates a careful presorting out from the refuse of particles that come from the dismantling of vehicles, machines, or big packages. The method is not applicable for use in a wide range of refuse as is found for example in business or in the private sector.
German patent document 3,601,175 describes a method and apparatus for separating various polymers out of a mixture of polymers. The method is based on the recognition that due to their nearly identical densities it is impossible in recycling plants to separate fractions of polypropylene and polyethylene from each other by a hydrocyclone sorting. In addition it has always been known that with the standard process for separating out and recovering thermoplastic resins from plastic garbage it is known to use staged different temperatures but the problem of separating the melted from the still foamed parts has no solution as yet.
The known process proposes, in order to separate from mixed polymers of small particle size polymers of roughly the same density but with different melting points, to load this mixture into a fast mixer and to plastify it by friction or heating the device to agglomerate the polymer particles with the lowest melting point, then to go to a cool mixer and then cool them into an agglomerate and separate out the unformed particles. Such a device has a fast mixer for heating the mixture to be separated, followed by a cool mixer whose output is connected to an air classifier which can be constituted as a known diffusor or impact separator or zig-zag sifter or flow reversing sieve. For the impact separation the polymer mixture is blown from a nozzle against an impact wall and over a sequence of recipients.
This method and apparatus are only applicable for use in an industrial setting and are only practical when used a lot.
German patent document 4,004,300 describes a method and apparatus for separating different plastic products. These are comminuted as is known, cleaned, and dried. The dried particles are fed to a heated movable support onto which the plastic particles with the lowest melting point stick and the particles with the higher softening point move along and can be separated. After the separation out of these particles the sticking particles are scraped from the steel belt.
This process and the necessary equipment require a great deal of regulated machinery that maintain specifically determined temperatures so that the installation is only operable in highly technical industrial settings. In addition the plastic particles must be cleaned before the treatment and comminuted and then put in a uniform thin layer on the heated support in order to avoid mistakes in the sorting. At the same time it is impossible to prevent that different plastic fractions treated by the known process contain a high portion of the wrong materials.
U.S. Pat. No. 4,374,573 describes a mobile apparatus for shredding refuse, in particular old tires. The shredder has several cylindrical cutter rollers with a plurality of cutter blades which rotate oppositely and which overlap. Means for further treating the comminuted rubber waste is not discussed.
U.S. Pat. No. 4,033,804 describes a method of and apparatus for recycling plastic refuse, in particular for treating molecularly stretched plastic containers. In one method for degluing adhered labels the plastic articles are heated about to the glass temperature and are thereby shrunk so that the labels separate from the shrunk plastic parts. The shrinkage amounts to at least 5%, preferably between 25 and 125% of the surface of the labeled article. Longer heating produces a further shrinking of the plastic parts. Further method steps for recycling the label-free plastic parts are not discussed in the document.
U.S. Pat. No. 3,814,240 describes a method of transporting a mixture of paper refuse with thermoplastic foil parts into a hot-gas stream. The method is aimed at the separation of paper and thermoplastic film refuse by the contraction of their specific surfaces to such an extent that the separation of the contracted plastic particles from the paper mixture can be achieved by standard mechanical methods, for example by air classifying or sifting. The method uses a feed conveyor, a hot-air producer, and a drying drum in which the mixture is heated to shrink the plastic parts. The thus treated articles are separated in a cyclone from the hot gas stream and are separated in an air classifier into heavy shrunk plastic particles and lighter paper waste. Discussion about a further treatment of these separated products is not found in the named document.
U.S. Pat. No. 3,883,624 describes a method of and apparatus for recycling foamed thermoplastic polymer refuse during the production of foamed thermoplastic plates. The refuse produced during the production of thermoplastic foam plates is ground up and fed onto a steel conveyor belt. As it moves through a heating zone at first it is melted and shrunk and then in a cooling zone it is subsequently embrittled, ground up, and finally mixed with fresh plastic granules. In this manner a 100% refuse-free reuse of the plastic production material is achieved.
German patent document 2,546,097 describes a method for treating the plastic refuse of if necessary presorted refuse. Such refuse materials can contain, in addition to plastic, specific light foreign materials such as textile or wood particles, kitchen refuse and the like. The described method is comprised of the following steps:
Then the pretreated refuse from step c) is separated in an inertial air classifier to separate out the foreign materials not embedded in the granulated plastic particles.
This method requires quite a bit of machinery so that it can only be logically used in a central treatment plant, not however in outside collection locations for example supermarkets or collection locations in the region of smaller communities or living areas. In addition the sorting of different types of plastics by the known method requires a substantial investment and energy so that its use is limited to large-scale commercial operations.
Stretched thermoplastics are used in plastic technology in many areas. They include above all the product group of fibers, films, foams, deep-drawn parts, blown bodies, and molded parts. A general characteristic of stretched thermoplastics is an orientation of the molecular chains. This orientation is created when the product is created by deformation procedures in the melting region or when cooled for example with fibers during spinning and stretching.
The discarded refuse products containing stretched thermoplastics are a particular problem in many cases because of their disadvantageous ratio of volume to weight, that is they take up a lot of space and weigh little. This affects handling them when collecting them for recycling as well as for treating and working on them in the recycling process. When dealing with foams and fibers these disadvantages are particularly noticeable.
Stretched thermoplastics relapse when heated to the condition they were in before being stretched, that is the stretched molecule chains relax back to nonstraight shape. The temperature region for this relaxation starts below the melting point of the thermoplastics. This means that this shrinking takes place before melting of the thermoplastics virtually without emitting anything.
In most cases the relaxation of the thermoplastics is accompanied by a drastic reduction of their elasticity which produces after cooling a notable brittleness.
When sorting plastic masses which are derived from the packing field there is the problem of plastic bonded to other materials. For example paper or cardboard, wood, or the like is frequently stuck to the plastic refuse.